First off, Sherlock and Wesley both constantly have to prove they're the best.
Also these beloved fools like to try and pick fights with people twice their size. Bonus! Aggressive! Swordsmen!
And they both have natural inclinations towards piracy.
Their ~significant others~ both look great when they angst.
But Buttercup and John aren't timid flowers, they'll fuck a bitch up. Especially when said bitch abandoned them in the worst possible way.
And though they both tried to move on.....
Disaster and terror...
...and maybe a few life threatening situations...
...have a way of reminding everyone what's truly important.
Err I guess also maybe friendship.